Top-dog pay at America's 500 largest companies collectively decreased last year for the first time since 2002, although the 13 female chief executives in that club are feeling rather flush.

After clocking a juicy 38 percent collective pay increase in 2006, CEOs of the 500 largest companies in the U.S. — as measured by a composite ranking of sales, profits, assets and market value — saw their compensation dwindle an average 15 percent in 2007. (Chalk up much of that volatility to performance-based compensation packages tied to flagging earnings and share prices.) Meanwhile, those lucky 13 saw their pay jump an average 27 percent.

Not that the pay gap between male and (the few) female CEOs doesn't persist. The average take, including salary and bonuses, for all 500 CEOs was $12.8 million — double the female average of $6.5 million.

Indra Nooyi surely isn't grousing about her paycheck. Topping the list of highest-paid female CEOs, the PepsiCo chief took home $12.7 million (including $4.5 million in bonus pay), putting her at No. 139 out of 500 chiefs overall. The Indian-born exec ranked a bit higher on the Forbes list of the most powerful women in the world, at No. 5.

Impressive as that sounds, Nooyi's total compensation was just one-fourteenth that of the highest-paid man on the list, Oracle's Larry Ellison, who took home a modest $1 million in salary but realized $182 million from the exercise of vested stock options last year.

Second on the list of highest-paid female CEOs is Avon Products' Andrea Jung, who banked $4.3 million in salary and bonus and received a total compensation of $12 million. Xerox Chief Anne Mulcahy came in third with total comp of $11 million, followed by Susan Ivey ($7.2 million) of cig-maker Reynolds American and Western Union's Christina Gold ($5.7 million).

Compensation experts won't hazard a guess as to when, if ever, that pay gap between male and female CEOs will close. They do, however, suggest that the ranks of female chief execs will continue to expand as more large companies look to boost diversity among senior-level management.

In one study of the largest companies (by sales), Catalyst, a nonprofit devoted to encouraging diversity in the workplace, found that the percentage of women holding corporate officer positions has increased to 15 percent from 12 percent in 2000. That means more women will be in a position to negotiate bigger paydays, says Mike Hodak, founder of management consulting firm Hodak Value Advisors.

"Boards are typically going to pay a premium for what they consider to be a brand name," says Hodak. "More and more women have a name in the world's largest companies. We're starting to see the benefits of them realizing that."

But it's not just a brand that big companies are looking for. "Often times they feel that women can bring that out-of-the-box thinking to the leadership role," says Hugh Shields, founding principal at C-level career consultancy Shields Meneley Partners. "They might have the relationship skills to drive a new culture and strategy through an organization."